Integration Testing

Integration Testing:

Testing data flow between dependent modules is called integration testing.

INTEGRATION TESTING is defined as a type of testing where software modules are integrated logically and tested as a group

It is also termed as 'I & T' (Integration and Testing), 'String Testing' and sometimes 'Thread Testing'.

The main function or goal of this testing is to test the interfaces between the units/modules.

The individual modules are first tested in isolation. Once the modules are unit tested, they are integrated one by one, till all the modules are integrated, to check the combinational behaviour, and validate whether the requirements are implemented correctly or not.

Here we should understand that Integration testing does not happen at the end of the cycle, rather it is conducted simultaneously with the development. So in most of the times, all the modules are not actually available to test and here is what the challenge comes to test something which does not exist!

Example:

Banking application:

Sc1: Login as user A, click on amount transfer link, enter the data to the required fields and click on transfer button. Login as user A, click on amount balance link verify the amount balance.

Why Integration Test?

    A Module, in general, is designed by an individual software developer whose understanding and programming logic may differ from other programmers. Integration Testing becomes necessary to verify the software modules work in unity

    At the time of module development, there are wide chances of change in requirements by the clients. These new requirements may not be unit tested and hence system integration Testing becomes necessary.

    Interfaces of the software modules with the database could be erroneous

    External Hardware interfaces, if any, could be erroneous

    Inadequate exception handling could cause issues.

    Modules also interact with some third party tools or APIs which also need to be tested that the data accepted by that API / tool is correct and that the response generated is also as expected.

Advantages

There are several advantages of this testing and few of them are listed below.

• This testing makes sure that the integrated modules/components work properly.
• Integration testing can be started once the modules to be tested are available. It does not require the other module to be completed for testing to be done, as Stubs and Drivers can be used for the same.
• It detects the errors related to the interface.

Challenges

Listed below are few challenges that are involved in Integration Test.

#1) Integration testing means testing two or more integrated systems in order to ensure that the system works properly. Not only the integration links should be tested but an exhaustive testing considering the environment should be done to ensure that the integrated system works properly.

There might be different paths and permutations which can be applied to test the integrated system.

#2) Managing Integration testing becomes complex because of few factors involved in it like the database, Platform, environment etc.

#3) While integrating any new system with the legacy system, it requires a lot of changes and testing efforts. Same applies while integrating any two legacy systems.

#4) Integrating two different systems developed by two different companies is a big challenge as for how one of the systems will impact the other system if any changes are done in any one of the systems is not sure.

In order to minimize the impact while developing a system, few things should be taken into consideration like possible integration with other systems, etc.

Types of Integration Testing

Big Bang Approach:

Here all component are integrated together at once and then tested.

Advantages of Big Bang approach:

• It is a good approach for small systems.

Disadvantages of Big Bang Approach:

Fault Localization is difficult.

    Given the sheer number of interfaces that need to be tested in this approach, some interfaces link to be tested could be missed easily.

    Since the Integration testing can commence only after "all" the modules are designed, the testing team will have less time for execution in the testing phase.

    Testing takes place at once only which thereby leaves no time for critical module testing in isolation.

Incremental Approach: which is further divided into the following

•  Top Down Approach
•  Bottom Up Approach
•  Sandwich Approach - Combination of Top Down and Bottom Up

Top Down Approach:

What is Stub and Driver?

Incremental Approach is carried out by using dummy programs called Stubs and Drivers. Stubs and Drivers do not implement the entire programming logic of the software module but just simulate data communication with the calling module.

Stub: Is called by the Module under Test.

“Stubs” can be referred to as code a snippet which accepts the inputs/requests from the top module and returns the results/ response. This way, in spite of the lower modules, do not exist, we are able to test the top module.

Driver: Calls the Module to be tested.

In simple words, DRIVERS are the dummy programs which are used to call the functions of the lowest module in a case when the calling function does not exist.

Both Stubs and drivers are dummy piece of code which is used for testing the “non- existing” modules. They trigger the functions/method and return the response, which is compared to the expected behaviour.

Stubs	Driver
Used in Top down approach	Used in Bottom up approach
Top most module is tested first	Lowest modules are tested first.
Stimulates the lower level of components	Stimulates the higher level of components
Dummy program of lower level components	Dummy program for Higher level component

Bottom-up Integration

In the bottom-up strategy, each module at lower levels is tested with higher modules until all modules are tested. It takes help of Drivers for testing

Diagrammatic Representation:

Advantages:

• Fault localization is easier.
• No time  is wasted waiting for all modules to be developed unlike Big-bang approach

Disadvantages:

 The higher level design flaws will be detected only at the end.

Top-down Integration:

In Top to down approach, testing takes place from top to down following the control flow of the software system.

Takes help of stubs for testing.

Diagrammatic Representation:

Advantages:

• Fault Localization is easier.
• Possibility to obtain an early prototype.
• Critical Modules are tested on priority; major design flaws could be found and fixed first.

Disadvantages:

• Needs many Stubs.
• Modules at a lower level are tested inadequately.

How to do Integration Testing?

The Integration test procedure irrespective of the Software testing strategies (discussed above):

1.   Prepare the Integration Tests Plan

2.   Design the Test Scenarios, Cases, and Scripts.

3.   Executing the test Cases followed by reporting the defects.

4.   Tracking & re-testing the defects.

5.   Steps 3 and 4 are repeated until the completion of Integration is successful